On 02/02/2012 08:04 PM, xancorreu wrote:
Al 02/02/12 19:30, En/na bearophile ha escrit:
xancorreu:
I get "segment violation" error with ./factorial 400000
How can I resolve it?
You are having a stack overflow. DMD currently doesn't print a good
message because of this regression that is being worked on:
http://d.puremagic.com/issues/show_bug.cgi?id=6088
On Windows with DMD you increase the stack like this:
dmd -L/STACK:100000000 -run test2.d 400000> result.txt
If it goes in overflow still, increase the stack some more. But it
will take a long time to compute the result even with the latest
2.058head with improved GC because the algorithm you have used to
compute the factorial is very bad.
I have rewritten your code like this:
import std.stdio, std.bigint, std.conv, std.exception;
BigInt recFactorial(in int n) {
if (n == 0)
return BigInt(1);
else
return BigInt(n) * recFactorial(n - 1);
}
void main(string[] args) {
if (args.length != 2) {
writeln("Factorial requires a number.");
} else {
try {
writeln(recFactorial(to!int(args[1])));
} catch (ConvException e) {
writeln("Error");
}
}
}
Note the usage of ConvException, it's a very good practice to never
use a generic "gotta catch them all" expression, because it leads to
hiding other bugs in your code, and this is a source for troubles.
Bye,
bearophile
Thank you very much for recode this. But you "only" put a "in" in
recFactorial function argument. What this mean? **Why** this is more
efficient than mine?
It is not. He just added some stylistic changes that don't change the
code's semantics in any way.
For the other hand, how can increase the stack in linux?
Thanks,
Xan.
I don't know, but it is best to just rewrite the code so that it does
not use recursion.
(This kind of problem is exactly the reason why any language standard
should mandate tail call optimization.)
